The present invention relates to the recovery of concentrated formic acid from biomass.
Biomass such as pulp, waste paper, paper mill sludge, urban waste paper, agricultural residues, rice straw, woody plant, cotton materials and cellulose fines from papermaking etc. may be reconverted into useful platform chemicals. This requires sufficient economics and reasonable process feasibility for the processes to be used for the recovery of industrially interesting chemicals.
A variety of interesting bulk chemicals is accessible by the acid-catalyzed hydrolysis of biomass such as cellulose which is a natural polymer consisting of glucose units and abundantly available on earth. One attractive option is the conversion of glucose to levulinic acid (IUPAC systematic name: 2-hydroxypropanoic acid i.e. 4-oxopentanoic acid i.e. acetyl propanoic acid) by acid treatment. In the following text, the trivial name levulinic acid is used as the name of this compound. Levulinic acid is a versatile building block for fuel additives, polymer and resin precursors.
Two different approaches are commonly applied for the acid-catalyzed hydrolysis of cellulose. The first one uses high concentrations of mineral acids (e.g., 15 to 16 N HCl or 31 to 70% by weight H2SO4) as catalysts at low operating temperatures (20 to 50° C.). The major drawbacks are the high operating cost of acid recovery and the use of expensive construction material for both the hydrolyser and the acid recovery system. The second approach uses highly diluted acids at high operating temperatures (170 to 240° C.). This method is favoured and research studies applying this approach are abundant.
There are several publications on conversion of biomass to carboxylic acids but none of them simultaneously recover both levulinic acid and formic acid economically and selectively with sufficient purity. Most of the publications disclose methods for converting carbohydrate material to organic acids such as levulinic acid and formic acid, and furfural. A purification process especially to formic acid is not described in the procedures of converting biomass in the literature.
Several publications disclose the separation and recycling of formic acid or more typically carboxylic acids in general, and levulinic acid or furfural from the mixtures thereof. The actual recovery of formic acid, and especially recovery of concentrated formic acid originating from biomass with suitable purity for further applications could not be found.
An example of a highly diluted acid process is disclosed in EP 365 665, EP 873 294 and by Hayes et al. in Kamm, Gruber, Kamm: Biorefineries—Industrial Processes and Products, Vol. 1, p. 139-164 and references therein. This is a commercialized technology that uses two-step hydrolysis with dilute mineral acid such as sulphuric acid to break down biomass containing carbohydrates to give intermediate chemicals such as hydroxymethylfurfural or furfural that can be further converted to levulinic acid and other chemical products such as tetrahydrofuran. Benefit of this biomass conversion process is to reduce the tons of trash in the nation's landfills, as well as reduce the dependence on imported oil used to produce petrochemicals. While levulinic acid can be synthesized by several methods, frequently they form large amounts of by-products and intractable materials, or require expensive feedstocks. However, because of its two-reactor system, this process eliminates many of the existing problems with levulinic acid production including by-product formation and the resulting separation problems.
EP 873 294 discloses a process wherein:
The carbohydrate containing material such as cellulose, hemicellulose and starch is mixed with an acid-water solution to form slurry.
Cellulose and starch containing carbohydrates such as glucose, galactose, or similar molecules are split into hexose monomers in acidic conditions. As the reaction continues at elevated temperature and pressure, the hexose monomers are converted to hydroxymethyl furfural and other intermediates and further into levulinic acid and formic acid. The reaction is carried out in a two-stage chemical reactor. The first stage is a short-contact tubular reactor operating at 210 to 230° C. and at a pressure of approximately 30 bar and a second stage reactor is a continuous stirred tank reactor with longer residence time operated at 195 to 215° C. and at a pressure of approximately 15 bar. If hemicellulose containing material is involved as feedstock, it is converted both to hexose and pentose monomers and oligomers. The pentoses degrade further to furfural.
The components with highest volatility, water, formic acid and furfural are vaporized and condensated from the mixture by adjusting the temperature and pressure.
The less volatile levulinic acid containing fraction is separated from lignin containing solid material by filtration.
In the article of Hayes et al. it is mentioned that the processing of cellulose yields approximately 50% of levulinic acid, 20% of formic acid, and 30% of tars calculated from the mass of 6-carbon sugars. The mass yield of furfural from 5-carbon sugars is approximately 50%. Thus, each ton of levulinic acid produced produces 400 kg of formic acid. There is clearly a need to recover efficiently and simultaneously formic acid parallel to the other platform chemicals.
US 2007/0100162 concerns the production of levulinic acid and discloses that the liquefication of lignocellulosic or cellulosic material can be facilitated by incorporating a solvent comprising furfural, levulinic acid, a compound obtainable from furfural or a compound obtainable from levulinic acid by various types of reactions, such as hydrogenation. The solid content can then be up to 50% in the feedstock while in EP 873 294 the slurry concentration of 20 to 40% was required. There is no teaching on how to recover concentrated formic acid from aqueous solution produced in this process.
U.S. Pat. No. 4,401,514 discloses a method for the recovery or extraction of chemicals such as furfural, formic acid, acetic acid and other organic chemicals from acidic hydrolysates of plant or vegetable matter. The object of this disclosure is to provide an extremely energy saving manner of extracting recovered furfural. During the furfural recovery steps of the method, a mixture containing furfural, formic acid, acetic acid and water is obtained. This mixture may further be distilled to separate an azeotrope of water and formic acid including some residual acetic acid and furfural and a mixture comprising furfural and acetic acid. In order to separate formic acid as a concentrated acid from its azeotrope, considerable additional amount of energy is required. Furthermore, there is no teaching on the influence or handling of levulinic acid if this should be present in such mixtures.
WO2005070867 discloses a reactive extraction method for the recovery of levulinic acid from an aqueous mixture containing e.g. levulinic acid, formic acid and furfural wherein the mixture is first contacted with a liquid esterifying water-immiscible alcohol in the presence of a catalyst at 50 to 250° C. to form esters of levulinic acid and formic acid. These esters remain in organic phase together with the alcohol and furfural. According to the invention, the desired levulinate and all the other compounds can be separated by applying different sequential separation methods, distillations such as e.g. reactive distillation from the organic phase. Formic acid ester is converted to formic acid by acid hydrolysis and separated simultaneously by distillation from the alcohol. This separation process has not been experimentally verified and is known to be very complex. Formic acid is equally obtainable as an ester from the organic phase requiring further processing for the recovery of the pure acid.
US 20030233011 discloses a method for treating a mixture obtained from biomass hydrolysis as follows: The solid phase is removed first and furfural is removed by decantation. Thereafter, the mixture comprising levulinic acid, formic acid and water is contacted with an olefin to form esters of levulinic acid and formic acid. These esters are then extracted with a water-immiscible organic solvent. After separating the aqueous layer, the esters are separated from the solvent by distillation and the extraction solvent is recycled. The solvent may be chosen so that it can be used as a fuel additive parallel to esters of levulinic and formic acid. The reaction with olefins can be made simultaneously with the extraction process according to the reference. This method does not involve recovery of formic acid in acid form.
U.S. Pat. No. 6,054,611 discloses a process operated at conditions with considerably lower temperatures than in EP 873 294, resulting in much longer reaction time and lower capacity. The separation of levulinic acid, furfural and water is performed by chromatographic methods. Conventional distillations are also mentioned in example 1, but the stream doesn't include formic acid. Levulinic acid is obtained as alkyl levulinate.
FI 117633 discloses a method for recovering and recycling a mixture of formic acid, acetic acid, water and furfural in the pulping process. This mixture does not include levulinic acid. The separation is carried out by a series of distillation columns using furfural as a distillation aid to separate the main part of water as furfural-water azeotrope. In the distillation, the said mixture incorporates several azeotropes making the distillation to pure products complicated. The mixture of formic acid and acetic acid is recycled to pulping process and it is neither disclosed nor considered relevant how to separate these acids as pure products.
In many cases, the carboxylic acids generated as the result of biomass degradation are obtained as dilute aqueous solutions. Distillation is an obvious method to purify isolated substances from aqueous solutions, but distillation as such is not the best option as far as energy-efficiency is considered. Besides, some of the components such as formic acid may form azeotropes with water making the separation into pure components difficult. The separation can be accomplished by arranging several distillation processes and equipment parallel or in series but then the energy cost of separation and equipment will become high. Furthermore, separation into single components is not feasible without using large columns with a high number of distillation stages or trays.
Separation of various chemicals may be based on liquid-liquid extraction processes. Even carboxylic acids have been separated from dilute aqueous solutions with extraction solvents insoluble or slightly soluble in water, or with solvent mixtures. However, the efficiency of extraction agents is typically not satisfactory enough to yield pure components.
U.S. Pat. No. 5,399,751 by contrast discloses a method for the recovery of formic acid from an aqueous solution containing acetic acid, formic acid and water. There is neither furfural nor levulinic acid present in this mixture. The procedure is described as follows: 1) The aqueous solution is contacted with a solvent consisting of mixed trialkyl phosphine oxides in a liquid-liquid extraction column producing two phases where the aqueous raffinate is low in acids and solvent. The aliphatic acids are extracted in the organic solvent phase. This solvent has a low miscibility and solubility in water. Cyanex 923 manufactured by Cytec Industries containing said mixture is used in the examples as the liquid extracting agent. 2) The solvent rich in acids is dehydrated to remove most of water in the first distillation column. 3) The bottoms of the first column is directed to second column in which the acids are stripped out from the solvent that is recycled back to the extraction stage. 4) The mixture of formic acid and acetic acid is splitted to separate fraction in the third distillation column. No advice is provided by this disclosure on the influence and possible treatment of mixtures containing chemicals such as furfural or levulinic acid, derived from biomass.
EP 0 038 317 discloses a method for the extraction of furfural, formic acid, and acetic acid from acid hydrolysates retrieved from biomasses, particularly from spent sulphate lyes. The distillate similar to the one disclosed in EP 873 294 from the hydrolysis reactor containing furfural, acetic acid, formic acid and water is subjected to liquid-liquid extraction. A mixture of trioctyl phosphine oxides in aliphatic hydrocarbon is applied as extracting agent for the extraction of mentioned organic compounds. Water is removed as the raffinate phase and the organic extractant phase is subjected to a series of evaporation and distillation processes to recover furfural and acetic acid as separate streams. The remaining impure mixture containing formic acid fraction is recycled back to biomass hydrolysis. Formic acid or concentrated formic acid is not obtained as a pure product.
The abstract of CN1254705 retrieved from WPINDEX AN 2000-506302 [46] discloses a method for separating and concentrating formic acid with phosphorus-contained extraction reagent in kerosene to prepare a solvent mixture. By distillation of solvent phase, the mass concentration of formic acid is more than 85% by this invention. The bottom solvent from distillation can be reused. The content of the original mixture and the effects of other components in distillation and extraction is not unveiled.
WO0146520 treats waste liquors containing carboxylic acids (mainly formic acid) and water and lignins and traces of furfural and acetic acid, from pulp production such as Milox and Acetosolv processes with extraction by ethers such as di-isopropyl ether. After the extraction the extracting reagent is distilled out from solution giving formic acid as the residual product. Formic acid and acetic acid are not separated. Further, furfural is mentioned but its behaviour and influence on distillation and extraction is not disclosed.
Several other publications are available on the separation of carboxylic acids and acid mixtures such as acetic acid and formic acid from aqueous mixtures thereof. None of these methods describe an economically feasible way to recover formic acid as concentrated acid from biomass or recovery together with levulinic acid and/or furfural from mixtures thereof.
In WO02053524 organic acids such as formic acid and acetic acid are extracted by ethers such as di-isopropyl ether (like in WO0146520). The extracting agent is recovered by distillation. The organic acids are recovered as the residue of distillation. In the separation of acetic acid from formic acid a distillation aid such as cyclopentane is used to break the azeotrope. Furfural is however not included.
The solution obtained from biomass degradation, such as hydrolysis at elevated temperature and pressure can contain furfural if the raw material includes pentoses. Furfural in these cases can be converted to its derivatives, such as furfuryl alcohol, methyl furfuryl alcohol, methylfuran, furoic acid, furfurylamine, furan, and their further derivatives. Catalytic hydrogenation of furfural to methyl furan and further into methyltetrahydrofuran or to furfuryl alcohol and further into levulinic acid is mentioned in the literature.
Prior art discloses several ways of recovering industrially valuable components from biomass degradation including furfural or levulinic acid. Aqueous carboxylic acids or mixtures thereof may be separated and/or circulated back to earlier processes stages. However, an economical and energy efficient method for technically feasibly recovering concentrated formic acid from a mixture containing other aliphatic acids such as levulinic acid and/or furfural that emerge in the reactive pre-treatment of biomass has not been available.
The dilute aqueous phase together with a mixture containing levulinic acid or levulinic acid and furfural together with formic acid has rendered it very difficult to recover concentrated formic acid economically from a mixture thereof.
The objective of the present invention is to economically and efficiently recover concentrated formic acid from a biomass degradation mixture.
A further objective of the present invention is to economically and efficiently recover concentrated formic acid together with levulinic acid and optionally furfural from an aqueous mixture thereof.